The present is invention generally relates to printing on a three-dimensional object. More specifically, this invention relates to an apparatus and method of printing a high quality image on a curved substrate utilizing a robotic system incorporating an ink jet printing head.
Molded plastic articles are becoming widely accepted as a replacement for metallic and glass articles. For example, panels of plastic materials, such as polycarbonate (PC) and polymethylmethyacrylate (PMMA), are currently being used to replace conventional glass windows and metal body panels in a variety of automotive applications, including components such as B-pillars, headlamps, windows, moonroofs and sunroofs. Automotive window systems represent a particularly desirable application for these plastic materials due to their many identified advantages, particularly in the areas of styling1 design, weight savings, safety and security. More specifically, plastic materials offer the automotive manufacturer the ability to distinguish their vehicles by increasing overall design and shape complexity. Being lighter in weight than conventional glass window systems, the incorporation of plastic window systems and components into the vehicle may facilitate both a lower center of gravity for the vehicle (and therefore better vehicle handling & safety) and improved fuel economy. Further, enhanced safety is realized, particularly in a roll-over accident because of a greater probability of the occupant or passenger being retained in a vehicle. Another advantage associated with plastic window systems is the ability to integrate several components (previously bonded or joined together) into one article, thereby reducing the number of assembly operations.
One inherent problem that with plastic window systems is the inability to easily print a high quality image on the resulting complex surface shape (concave, convex, multiple curvature, etc.) of the article. Printing is desirable since other means for creating images on the surface of complex three-dimensional articles are time consuming. Unfortunately, common two-dimensional printing methods, such as screen-printing and pad-printing, have only been able to meet this need with limited success.
An image may be printed directly onto either surface of a two-dimensional article using an ink or paste and various methods known to those skilled in the art. In addition to the above mentioned methods, other methods include screen-printing, ink jet printing and automatic dispensing (such as drip & drag, streaming, and simple flow dispensing). In each of the above instances, the shape of the panel impacts the quality of the printed image, for example, screen printing and other methods become very difficult on non-planar panels. The speed at which printing is done also affects the quality of individually printed lines or features, and therefore the resultant image. Slower speeds and higher flow rates for the ink or paste can result in wider and thicker features of the image. Conversely, higher speeds and slower flow rates can result in slimmer and lower features. Further, maintaining an appropriate off-set distance between the printing device and the surface of the article becomes more difficult as complexity of the surface shape increases, but maintaining a proper off-set is necessary to ensure a high quality image. One additional concern is being able to easily adapt the printing system to different shaped articles, as opposed to having to construct, for each new article design, a new printing system which is dedicated to that specific article.
Accordingly, there exists a need to provide an improved apparatus and method for printing an image on the surface of a three-dimensional article or substrate, such as a plastic automotive window.